1. Field of the Invention
The present invention relates to a plug for cells of electrical storage batteries.
In particular, the present invention relates to a plug for cells of electrical storage batteries, particularly suitable for industrial lead/acid storage batteries, with centralized inseries self-levelling of the electrolyte, with independent gas vent for each cell, with pressure-retention of filling-up water and with the possibility of immediate optical check.
2. Description of the Prior Art
It is known that the cells of any electrical storage battery consume a certain amount of water, both because of water dissociation related to the loss in charge efficiency, and the entrainment by the gases during the overcharging period, as well as due to evaporation, in particular in industrial storage batteries, for instance for automotive uses, because they undergo intense daily, or even more frequent, charging and discharging cycles, with rather high operating temperature.
As each storage battery contains a rather high number of cells, the maintenance of the right electrolyte level in each cell requires a great deal of care this operation being essential to the purpose of maintaining at the correct value the density or concentration of active electrolyte, in particular of sulphuric acid, in the case of the most widely used storage batteries, the so-called "lead/acid" type. Thus it has not been easy to accomplish this object and, anyway a considerable time waste and hence a high cost has been involved.
Furthermore, the vent stacks of the cells not always can be easily reached and it is even less easy to inspect them, so that a correct levelling is an operation difficult to be performed from the technical viewpoint. On the other hand, an incorrect levelling of the electrolyte causes decreases of unpredictable seriousness in storage battery life, whether the electrolyte level decreases under the upper edge of the plates, or the excess of electrolyte overflows on the covers and enters the containing boxes, creating insulation losses, corrosions of the vehicle and the floors, and rendering completely unbalanced the capacity ratio of the individual cells.
The seriousness of the problem, not always correctly realized by the user, has induced the manufacturers of electrical storage batteries to study automatic levelling systems. So, numerous types of plugs for cells of electrical storage batteries have been proposed, but none of them has allowed the problem to be overcome to a complete and satisfactory extent.
Among the various solutions proposed, we mention the automatic, individual, portable filling-up devices, connected to the water supply system or to the reservoir of distilled water, which can flow through the vent stack of the individual cell until one of the various shutting systems, actuated by the electrolyte level, discontinues the feed when the desired level is reached.
This levelling system allows the errors of excessive, too low, or different levelling to be eliminated with a considerable technical advantage, but does not overcome the difficulty which is met in reaching many vent stacks, which can be positioned in even inaccessible places, without removing the storage battery, nor does it anyway overcome inconveniences, time waste and related increase of operation cost.
Also various types of centralized self-levelling plugs are known, in which the distilled water supply is connected to an end of one of the plugs, each plug being then connected in series or in parallel to all other plugs.
For such a system to operate perfectly a sensor of electrolyte level is required, which should be capable of shutting the feed bores leading to each individual cell, and which can lead water to the subsequent cell, as soon as the correct level is reached.
The various types of centralized self-levelling filling-up devices of the prior art can be subdivided mainly into two categories: plugs requiring tight cells, for which the feed pipe is also the vent pipe for the (potentially explosive) gases produced inside the cells, and plugs which do not require tightness, so that gases can escape to the outside from each individual cell.
Plugs belonging to the first category, in which the shutting occurs due to water surface tension, have the advantage of not containing moving parts, but are affected by the serious hazard that the electrical storage battery or a set of the cells may behave as one single explosion chamber in case of sparking, which is particularly dangerous if occurring inside the cell.
The plugs of the second category comprise some types in which the level-sensing element, which causes the feed to be discontinued, is constituted by a very small difference in electrolyte level which occurs in the interior of the feed plug when the correct level is reached, and which balances a small difference in level in the interior of the supply reservoir positioned at that time above the storage battery. This system is very delicate, and involves moving the water reservoir each time the storage battery must be charged,
Other plug types known in the prior art exploit the technique of floats, the rising of which closes, by a pin, a small feed bore, which can extend in a vertical and/or in a horizontal position. Fastened to the float, an optical signalling means is installed, which consists of the head of a small rod, or of a small disc on a lever, which becomes visible on the plug surface, when the electrolyte level reaches its correct value. Around the moving elements the gas flows towards the outside, and inside a cavity, provided laterally to the float-controlled rod, a guard hole is provided, often in a very inconvenient place. However, in all these types, it is the small thrust, applied by the float, which retains the pin inside the feed nozzle; such an arrangement involves considerable risks of insufficient tightness, both due to manufacturing defects, and because of the occurrence of small deposits of debris arising from the breakdown of the plates, due to entrainment by the evolving gases.